AB5 toxins produced by pathogenic bacteria comprise an A subunit with enzymic activity and a pentameric B subunit responsible for interaction with glycolipid receptors on target eukaryotic cells (1). The three AB5 toxin families recognised to date are the Shiga toxins (Stx), Cholera toxin (Ctx) and the related Escherichia coli heat labile enterotoxins (LT), and pertussis toxin (Ptx). In each case, they are key virulence determinants of the bacteria that produce them (Shiga toxigenic E. coli [STEC] and Shigella dysenteriae, Vibrio cholerae and enterotoxigenic E. coli [ETEC], and Bordetella pertussis, respectively). Collectively, these pathogens cause massive global morbidity and mortality, accounting for millions of deaths each year, particularly amongst children in developing countries. The AB5 toxins exert their catastrophic effects by entering their respective target cells (usually by receptor-mediated endocytosis), and then inhibiting or corrupting essential host functions. The A subunits of Stx toxins have RNA-N-glycosidase activity, and cleave 28S rRNA, thereby inhibiting host protein synthesis. The A subunits of Ctx/LT and Ptx are ADP-ribosylases which modify distinct host G proteins, resulting in alteration of intracellular cAMP levels and disregulation of ion transport mechanisms (1).